Filox should be backwashed at flow rates that vary with temperature, not pressure. The Fleck DLFC button will adjust to be fairly accurate even in varying pressures. We set Filox systems at 20+ GPM per square foot. I would bump it up to 15 GPM since your pump can handle it. The frequency can probably be adjusted to less, 2-3 days between backwashes. The Fast Rinse can also be adjusted down considerably, especially considering the higher DLFC flow rate. I would recommend less than 5 minutes for the fast rinse cycle.
Sounds like you did your research,